1. Field of the Invention
The present invention relates to a signal receiving apparatus and a receiving method, and in particular to a television signal receiving apparatus which performs filtering of a received signal and a receiving method.
2. Description of Related Art
A fixed-length packet with 188 bytes is used for “Transport Stream (TS), a packet transmission format used in digital broadcasting and the like, and it makes it possible to periodically transmit information for enabling decoding even when receiving is started in the middle of a program, in addition to image information and audio information. Such information is referred to as “service information (SI)” or “program specific information (PSI)”. It is assumed that SI in the description below includes PSI.
In a digital broadcasting system, it is identified by a receiving side (a decoding side) what kind of information each received packet has, from an identifier (PID) each packet has, in order to acquire the information. However, as for SI, the receiving side does not have to always acquire it. For example, the receiving side may require SI only when the SI has been updated. In this case, whether SI has been updated or not is identified from a history number (version) added to the SI.
It is also possible to mix multiple pieces of SI in one packet, and multiple pieces of SI may be transmitted with a packet with the same PID. In this case, the table number added to SI is used to identify SI.
Hereinafter, the data structure used when SI is transmitted is referred to as a “section”, and data transmitted with a section is referred to as “section data”. The method of transmitting multiple pieces of SI mixed in one packet is called multi-section transmission or the like.
Accordingly, in packet decoding processing by the receiving side, at least the following two types of filtering are required.
(1) Filtering for extracting a desired packet from received packets based on a PID (hereinafter referred to as “PID filtering”); and
(2) filtering for extracting desired section data if an extracted packet has a section (hereinafter referred to as “section filtering”).
A filter used for section filtering is referred to as a “section filter”. Extraction conditions are set in advance in the section filter, and such section data as satisfies the extraction conditions is extracted from a packet extracted by PID filtering. As the extraction conditions, an “AND condition” (also referred to as a “reference condition” or the like) for specifying the pattern of section data to be extracted and a “MASK condition” for excluding a part of the AND condition are set. Section data is extracted from a packet based on the AND condition and the MASK condition (for example, Japanese Patent Laid-Open No. 2000-22747).
A filter used for PID filtering is referred to as a “PID filter”.
Recently, it has become possible to further specify a “NOT condition” as an extraction condition in order to extract a pattern which is unmatched with a part of an AND condition. As operation specification of a section filter, the following two are conceivable according to the usage of the NOT condition.
Specification 1: To detect a pattern in which at least 1 bit specified with a NOT condition is unmatched with an AND condition.
Specification 2: To detect a pattern in which all the bits specified with a NOT condition are unmatched with an AND condition.
In section filtering, there are two cases: a case where extraction of section data based on the specification 1 is required and a case where extraction of section data based on the specification 2 is required.
However, when a section filter which operates in accordance with the specification 1 is used, it is not possible to extract section data in which all the bits specified with a NOT condition are unmatched with an AND condition by performing section filtering once.
Meanwhile, when a section filter which operates in accordance with the specification 2 is used, it is not possible to extract section data in which at least one bit specified with a NOT condition is unmatched with an AND condition by performing section filtering once.
Furthermore, in the case of a section filter to which a NOT condition is applied, one type of operation specification must be fixed for one section filter.
As a result, in order to extract desired section data, section filters with multiple specifications are required, or it is required to perform section filtering multiple times. That is, there is a problem that the circuit scale of a receiving apparatus is increased or that the number of section data which can be processed per unit time is decreased.